Everyone makes mistakes and developers are no different. As a developer, you spend a significant portion of your time debugging the code you write. It's an inextricable aspect of software development. Some bugs are easy to find while others can make you scratch your head.
Xcode offers developers a mature development environment with a powerful debugger. Under the hood, Xcode's debugging tools take advantage of LLDB, the debugger of the LLVM project. It isn't necessary to have a deep understanding of LLDB or LLVM to make use of Xcode's debugging tools, but it certainly doesn't hurt to become familiar with LLDB and LLVM.